_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

The main Groups IV and V
Ph 2 BiBiPh 2 no compounds containing Bi-Bi bonds are known. We shall
therefore concentrate our attention on the derivatives ofphosphorus and arsenic.
Diphosphines and diarsines are readily oxidized in air, the tetramethyl
compounds being spontaneously inflammable. The P-P or As-As bond is
readily cleaved by a variety ofreagents. Some ofthese reactions are exemplified by
tetraphenyldiarsine.
Ph3As+As o Ph2 AsX
300C
Hal 2
Ph2 As O(OHl+(Ph~sJ 2 0
(Ph2As)2 S
20 ,fi20
s
Ph2AsAsPh2
Mei
Ph 2Me 2As+I- + P~Asl
Na/K
Ph2AsM'
When difunctional compounds RMX 2 (X= H, Hal, M', NR~) are used in the
preparations listed above, cyclic oligomers (RP)n and (RAs)" are generally
obtained. Polymeric forms are also known. Rings with three, four, five and six
annular atoms ha ve been obtained with a variety of alkyl, aryl and perfluoroalkyl
substituents. There is evidence from 1 H n.m.r. measurements of larger rings.
Polymethylarsine (MeAs )" prepared by the reduction of methylarsonic acid with
H 3 P0 2 exists in several forms. One is a yellow oil, m.p. l2°C, b.p. 118-120/
1 mm, which is pentameric (MeAs) 5 in the solid state. The pentamer is also the
major component in solution and in the vapour phase. The ring is puckered. A
second purple-black form, m.p. 204°C, has an unusualladder structure. Double
chains of trans-As 2 Me 2 units are joined by long As··· As links. The compound is
both a semiconductor and a photoconductor. Unlike (MeAs) 5 which is rapidly
oxidized, the ladder form is stable to air. The phenyl derivatives (PhP)" and
(PhAs)n were originally formulated as PhM=MPh, analogous to azobenzene.
They are now known to be either cyclic oligomers or chain polymers. X-ray
diffraction has shown that the main form of arsenobenzene, m.p. 212°C, consists
of six membered rings in the chair form with phenyl groups in equatorial
positions. One form of phosphobenzene m.p. 19 5-9°C has a similar structure,
and another, m.p. 148-150°C, is a cyclic pentamer.
An example of an arsenobenzene which is apparently a long chain polymer
is Salvarsan or Arsphenamine. This results from reduction of 3-nitro-4-
hydroxyphenylarsonic acid.
142
Salvarson